Example 1: You can add water to concentrated orange juice to dilute it until it reaches a concentration that is pleasant to drink.
Example 2: Pure oxygen is too rich for us to breathe for long, leading to problems such as hyperoxia.
In the air around us, oxygen is diluted naturally by the presence of nitrogen. Deep sea divers are harmed by nitrogen in the air, because deep under the sea gas pressures increase, and at higher pressures nitrogen causes an agonizing condition in divers called 'the bends.' For this reason, deep sea divers breathe oxygen diluted with helium rather than nitrogen.